1. Field of the Invention
The present invention relates to a pneumatic control device for a hydraulic power tool, and the pneumatic control device is operated by one hand.
2. The Prior Arts
Heavy equipments, such as dump trucks and cranes, are often used during constructions or civil engineering. In order to provide powerful output, hydraulic power is chosen for the heavy equipment. The hydraulic power system needs a motor to pressurize the hydraulic fluid to drive the hydraulic power tool. The motor can be an electric motor or an internal combustion engine. In the civil engineer, it is usually the combustion engine. Before the hydraulic power tool is operated, the combustion engine has to be activated or the power generated by the combustion engine is supplied to a pump device which provides the pressurized hydraulic fluid to the tool. After the jobs of the tools are finished, the connection between the combustion engine and the pump device is cut off by operating a clutch-like mechanism to stop the working of the pump device.
A conventional engineering tool is equipped with an operation control device, and thus the users can use the operation control device to operate the hydraulic power tool. Some of the operation control devices are operated by electricity and some of the operation control devices are operated by pressurized air. For engineering vehicles, the pneumatic device is basic equipment so that using the pneumatic device to control the hydraulic power tools is a proper choice. The conventional pneumatic control device has a power control rod and a direction control rod. The power control rod controls the pressurized air to be sent to the pneumatic power tools and controls the connection between the combustion engine and the pump device. The direction control rod controls the direction that the pressurized air provided to the pneumatic power devices so that the pneumatic power device controls the direction that the hydraulic power tools work. Generally, the power control rod is used to control the operation of the pressurized air which is provided to the connection between the combustion engine and the pump device. The direction control rod is then used to control the direction that the hydraulic power tool moves. There is a stop position for the hydraulic power tools so that when the tools are not in use, the tools can be positioned at that position. For example, the dump truck lowers its bed to the lowest position when not in use. After the work of the hydraulic power tool is finished, one control rod is operated to stop supplying the pressurized air and the tool would be back to its stop position by gravity. However, there are two control rods to operate two operations, respectively. The users may frequently forget to operate the other control rod to disengage the combustion engine from the pump device.
In order to overcome the shortcomings mentioned above, the applicant brings up a granted patent (Application No. TW87200342) (the first patent hereinafter). However, the structure of the first patent is still complicated. Thus, in order to reduce the manufacturing cost, the applicant brings up a second granted invention (Application No. TW91204509) (the second patent hereinafter). The second patent allows the user to operate the two rods to simultaneously stop the hydraulic power tools and the pressurized air. Furthermore, the direction control rod is simplified so as to have the benefit of low manufacturing cost. Nevertheless, the first and/or the second patents have two control rods (the power control rod and the direction control rod), and a connection device is needed to be connected between the two rods so that the structure is still complicated. If the users want to operate by one hand, the hand has to be moved between the two rods and this is not convenient for the users.